Respiratory interfaces, e.g., nasal cannulas are used to deliver respiratory gases for therapeutic effect, including oxygen therapy, treatment for sleep apnea, and respiratory support. Small nasal cannulas are commonly used for delivery of low volumes of oxygen. Sealing nasal cannulas, such as the cannulas disclosed in U.S. Pat. No. 6,595,215 to Wood, are used for the treatment of sleep apnea. However, treatment with certain types of nasal cannulas may be limited by the lack of information available on important treatment parameters. These parameters include information regarding the gases within the user's upper airway, such as pressure, flow rate, and carbon dioxide build up. These and other data may be useful in judging the efficacy of treatment as well as for controlling and monitoring treatment.
In addition, prior art nasal cannula designs (especially those designed for neonatal oxygen therapy) may undesirably create a seal with the user's nares, which may have detrimental effects on the user's health.
Oxygen (O2) therapy is often used to assist and supplement patients who have respiratory impairments that respond to supplemental oxygen for recovery, healing and also to sustain daily activity.
Nasal cannulas are generally used during oxygen therapy. This method of therapy typically provides an air/gas mixture including about 24% to about 35% O2 at flow rates of 1-6 liters per minute (L/min). At around two liters per minute, the patient will have an FiO2 (percent oxygen in the inhaled O2/air mixture) of about 28% oxygen. This rate may be increase somewhat to about 8 L/min if the gas is passed through a humidifier at room temperature via a nasal interface into the patient's nose. This is generally adequate for many people whose condition responds to about 35-40% inhaled O2 (FiO2), but for higher concentrations of O2, higher flow rates are generally needed.
When a higher FiO2 is needed, one cannot simply increase the flow rate. This is true because breathing 100% O2 at room temperature via a nasal cannula is irritating to the nasal passage and is generally not tolerated above about 7-8 L/min. Simply increasing the flow rate may also provoke bronchospasm.
To administer FiO2 of about 40% to about 100%, non-re-breathing masks (or sealed masks) are used at higher flows. The mask seals on the face and has a reservoir bag to collect the flow of oxygen during the exhalation phase and utilize one-way directional valves to direct exhalation out into the room and inhalation from the oxygen reservoir bag. This method is mostly employed in emergency situations and is generally not tolerated well for extended therapy.
High flow nasal airway respiratory support (“high flow therapy” or “HFT”) is administered through a nasal cannula into an “open” nasal airway. The airway pressures are generally lower than Continuous Positive Airway Pressure (CPAP) and Bi-level Positive Airway Pressure (BiPAP) and are not monitored or controlled. The effects of such high flow therapies are reported as therapeutic and embraced by some clinicians while questioned by others because it involves unknown factors and arbitrary administration techniques. In such procedures, the pressures generated in the patients' airways are typically variable, affected by cannula size, nare size, flow rate, and breathing rate, for instance. It is generally known that airway pressures affect oxygen saturation, thus these variables are enough to keep many physicians from utilizing HFT.